The patent application, filed on June 21, 1967, succinctly explains how a mouse works: “An X-Y position indicator control for movement by the hand over any surface to move a cursor over the display on a cathode ray tube, the indicator control generating signals indicating its position to cause a cursor to be displayed on the tube at the corresponding position. The indicator control mechanism contains X and Y position wheels mounted perpendicular to each other, which rotate according to the X and Y movements of the mechanism, and which operate rheostats to send signals along a wire to a computer which controls the CRT display.”

Give or take a few technological advances, that’s still how a mouse works.

Not only did this demo mark the debut of the mouse, but also hypertext, shared-screen collaboration, object addressing and dynamic file linking—basically everything that keeps the corporate world churning along today. You can watch the Mother of All Demos in its entirely on YouTube.